One component of many microfluidic processes is a plurality of monodisperse droplets. To form a plurality of droplets with traditional techniques, a brute force approach is generally used. For example, in some processes, each desired combination of reagents must be emulsified individually using a single microfluidic droplet maker; the products of all emulsifications are then pooled together to create a single emulsion library. This can be a long, tedious, and expensive process for even small libraries. Moreover, because of the sequential, manual emulsification of each element, it can be very difficult to maintain high uniformity in droplet size.